This is a subject that is very near and dear to my heart. I lost my mother in 1990 and it is now 2007 and there is stilll a big hole in my life and heart. When you lose your mother, like you said, you lose your best friend. Your mother nurtured you, gave birth to you, and was there whenever you needed her.
I also took care of my mother towards the end, I look back now and think of how special those times were. I am very proud that I did all I could for her and I know she was thankful, even if she didn't say it all the time.
You will never get over it, no matter what other people say, I am 45 yrs old and miss her everyday and ya know sometimes, it may seem weird, but I ask her things and talk to her, and I feel better.
I am very proud of you for doing the best you could and I am sure your mother is watching over you, her angel, and giving you strength to live day by day.
She will always love you and you her, that is the special bond between a mother and a daughter, that never ends.
Hang in there, you have all my sympathy and best wishes.
Let the tears roll, when they don't, there is a problem.